Well, my concept was that the scouts would have carte blanche to do just about anything in the name of preserving a planet's native environment; any native sentients / sophonts, native species, native climate and so forth. And when a pirate or other undesireable (maybe a Zho or Soli doing "behind the lines black ops") came to the fore, and if the army, navy and marines couldn't handle it (too distant, too busy, or some other factor or combination thereof), then the Scouts'd zoom in and take care of business.
I wrote a piece of Traveller fiction (which I've not published) where a drug lord had a treaty prohibiting army, marines and various other ground military from interceding on his world. The story ended with a few platoons of Naval Infantry led by a Scout Flight Captain to take care of business.
In tight situations, and given that the scouts go where others don't, it was my thinking that the IISS would have it's own special elite units. Heck, maybe they got some psi-talented people in their ranks who can do the Zho thing of teleporting in, shooting things up, rescuing whoever, and then teleporting out.
Man ... I sure could go for some Taco Bell right now.